The goal of this project is to study three aspects of the processes by which porphyrins may be effective, both in location and regressions of tumors: (1) the aggregation processes of porphyrins in aqueous solutions; (2) the binding and incorporation of the porphyrins from the aqueous phase into membranes using liposomes as models; and (3) the possible use of liposomes as porphyrin delivery systems. The study is aimed at the molecular level. If successful, the elucidation of the increased affinity of porphyrins to malignant vs. normal tissues might lead to improving the diagnostic and therapeutic role of this phenomenon.